Forming stripes of magnetic material



Feb. 27, 1962 Filed Dec. 2, 195a '2 Sheets Sheet 1 m z z zamL m amass .z LEV/NE ATTORNEY Feb. 27, 19 R. H. co w|| ETAL FORMING STRIPESOF' MAGNETIC MATERIAL 2 Sheets-Sheet 2 Filed Dec. 2, 1958 RICHAAIE IE ZBZiv/LL m CHARLES] LEVINE Y B QW W W \|l..... mm mm Q ATTORNEY This invention relates to methods of forming a stripe of magnetic material, and more particularly to forming an adherent and coherent magnetic stripe, or several such stripes when desired, on a surface of a relatively wide paper web. For magnetic data storage on paper it may simplify the recording and retrieval of the data to have a number of separate narrow stripes of magnetic material on the paper rather than a single magnetically responsive coating covering the paper surface. Stripes also have a better appearance than an entire coated surface, leave the uncoated portions available for written or printed matter, are better for the handling and folding characteristics of the paper and economize in the consumption of magnetic material.

Tape which carries on one surface particles of ferromagnetic material has been produced in large quantities for use in the magnetic recording or storage of information which may take the form of audio signals, pulsecoded data, or the like. One known method for produc ing a magnetic coating utilizes a coating composition made up of iron particles ground in a volatile organic solvent vehicle containing a polyvinyl acetate resin. This composition can be applied by a reverse roll coater to a paper tape. Evaporation of the organic vehicle with due care in the handling of the tape and disposition of the vapor leaves a coating of iron particles in a resin film, forming a sound-recording track covering one side of the tape. This procedure, however, involves the use of rather expensive and potentially hazardous organic solvents, which must be removed before the filrn-forrning material becomes fixed on the tape. This type of coating composition also tends to spread laterally to an excessive degree if it is attempted to apply a relatively narrow stripe to a longitudinally extensive web. This flow characteristic and other characteristics raise problems if it is attempted to adapt such compositions for use in a method of forming magnetic stripes on paper.

Also known are a variety of pigmented paper-coating compositions having water rather than an organic liquid as the vehicle, some of which utilize a synthetic latex dispersion to carry the pigment. Conventional apparatus of various types commonly is used to apply the coatings, including wide rolls which rotate in a sense opposing the direction of paper travel to transfer to a wide paper web the coating composition which has been measured onto the rolls. However, the use, in the production of stripes on a paper web, of liquid coating compositions with water as the vehicle, as with those having an organic liquid vehicle, also introduces problems although somewhat different in nature involving the handling, control, and removal of the vehicle during drying, the control of viscosity, and the presence, absence, or magnitude of certain other properties such as thixotropy which affect the ease and success of the striping operation. The known water base compositions are not adapted for magnetic striping, and they contain neither the ferromagnetic substances nor certain other component materials which have been found to contribute properties of great utility when use is contemplated in forming stripes of magnetic material on a paper web.

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Other types of magnetic-striping procedures are possible. For example, a waxy or resinous composition containing iron particles may be heated and extruded as a molten strip onto the moving Web. In this case there is no liquid vehicle to handle, but again problems arise, for example in the provision and control of heating and extrusion procedures and in the formulation of a suitable extrudable magnetic composition.

Thus it'is found that, in dealing with any method of forming a magnetic stripe on paper, difficulties present themselves in the procedures and' concomitant magnetic formulations used for applying and fixing the striping material. With coating compositions utilizing a liquid vehicle, the procedures involved in moving the liquid composition onto a suitable transfer surface for carrying the liquid to the paper, moving the paper web past the surface to pick up the liquid, and fixing the composition in solid form on the paper should be properly coordinated with the choice of the coating composition itself. This is necessary if there is to. be obtained a desirable result, including among other considerations an adequately heavy coating in a narrow stripe which is satisfactorily rich in material of good magnetic properties, sufficiently thick for the contemplated magnetic storage purposes, closely controlled in width, coherent, and adherent to the paper but without weakening the underlying structure of the paper web. A method suitable for obtaining such a narrow stripe, employing fully adequate transfer techniques in combination with the use of a satisfactory aqueous magnetic striping composition, has not heretofore been perfected or proposed.

Accordingly, it is an object of the present invention to provide a new and improved method of forming a stripe of magnetic material which avoids one or more of the disadvantages of the methods available in accordance with prior art practices.

It is another object of the invention to provide a new and improved method of forming a stripe of magnetic material which utilizes an aqueous composition for providing a stripe rich in materials giving high magnetic response characteristics, in association with techniques of applying such an aqueous composition which are readily controllable to obtain a narrow stripe of the desired dimensions and physical properties. 7

It is a further object of the invention to provide a new and improved method of forming a magnetic stripe on a paper web utilizing inexpensive raw materials which do not require an organic solvent vehicle and which are applied to and fixed upon the web by the use of procedures which do not require a very complex apparatus.

It is still another object of the invention to provide a method of magnetic striping which combines techniques and formulations heretofore unrecognized as valuable for this purpose.

It is yet another object of the invention to provide a new and improved method of forming a magnetic stripe of superior qualities which utilizes aqueous magnetic coating compositions to obtain in a single application a heavy coating in a narrow stripe which is rich in material of desirable magnetic properties, sufiiciently thick for efficient magnetic storage of information, easily and closely controlled in width, smooth and coherent, and strongly adherent to a paper substrate. 7

In accordance with the invention, the method of forming a stripe of magnetic material on one surface of a relatively wide paper web comprises moving the other surface of the paper web in a predetermined direction over a guiding surface, arranging transfer means, having a cylindrical peripheral surface narrower than the width of the stripe to be formed, with this peripheral surface disposed closely adjacent to the aforementioned one web surface opposite the guiding surface, the transfer means being supported on a central axis which is disposed in a plane parallel to the one web surface passing the guiding surface but perpendicular to the direction of motion thereof, and rotating the transfer means about the central axis in the sense causing the peripheral surface to move, while adjacent to the one web surface, in the direction opposite to the direction of motion of the web. This same method further comprises applying to the peripheral surface as it approaches the web surface a coating composition of an aqueous synthetic latex dispersion which contains particles of ferromagnetic iron oxide in suspension and a thickening agent, and subjecting the web, carrying a wet stripe of the magnetic composition transferred from the peripheral surface, to drying conditions at elevated temperatures to provide a deposit free of tack and resistant to blocking and smudging under dry and under humid conditions.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the drawings,

FIG. 1 is a flow sheet depicting a method embodying the invention of forming a stripe of magnetic material onan elongated paper web, and certain apparatus, representative of numerous forms of equipment which can be used as aids in carrying out some of the several steps in this method, is illustrated schematically at various points in the flow sheet;

FIG. 2 is a detail, partly in schematic representation, of the portions of the flow sheet of FIG. 1 which indicate the procedures involved in handling the magnetic material in a liquid vehicle and applying it to the paper web; and

FIG. 3 is another View, showing representative apparatus useful in carrying out the steps of the method at the point of application of the magnetic material, and taken in the direction indicated 3, 3 in FIG. 2 so as to omit showing the paper web as it passes that point.

Referring now to FIG. 1, there is indicated a supply roll 11 of an elongated continuous paper web 12, which, for example, may be of ledger paper stock about 14 inches wide and weighing 32 pounds per ream figured on the basis of SOD-sheet reams of 17 x 22 inch sheets. The supply roll unit ordinarily is provided with an automatic brake, not shown, and the paper web passes over idler rolls, not individually identified, wherever necessary or convenient as it is unwound and travels through the various operations. As it happens to be shown schematically in FIG. 1, the inside surface of the web 12 as it comes off the supply roll is the surface to which stripes are to be applied; this surface will be identified for convenience in the following description as the one surface of the web, while the reverse surface, which happens to face toward the outside of the supply roll in the particular diagrammatic showing of FIG. 1, will be called the other surface of the web.

The method in accordance with the invention of forming a stripe of magnetic material on the one surface of the relatively wide paper web 12 comprises moving the other surface of the paper web in a predetermined direction over a guiding surface 13. The stripe to be formed ordinarily is quite narrow, especially when compared to the Width of the relatively wide web, which ordinarily is considerably more than several inches in width. A stripe of the order of 0.100 inch in width has been found to be useful for recording data in the form of binary code pulses closely spaced longitudinally along the stripe, and a typical tolerance for the width of such a stripe formed by the method of the present invention is plus or minus 0.005 inch. The web is caused to unwind and move by pulling over a feed roll, indicated at 14 near the other end of the flow sheet, which is driven in the sense indicated by the arrow along side the roll 14. A number of rubber friction idler rolls, not indicated in the drawing, may be provided topress against the free surface of the web as it passes over the feed roll 14 to insure sufficient traction for unwinding the web and moving it over the guiding surface 13 and through the subsequent operations. The guiding surface 13, as shown for the embodiment depicted in FIG. 1, is at any instant the portion of the periphery of an impression roll 16 which at that instant is adjacent to a transfer means or applicator indicated gen erally at 17 in FIG. 1. The impression roll 16 is driven in the sense indicated by the arrow alongside the roll to aid in moving the web. As illustrated schematically in FIG. 1, the direction of motion of the web is toward the upper left as it passes around the portion of the roll 16 which is serving as the guiding surface 13. It can be seen that it is the other surface of the web which moves over and in contact with this surface 13.

The transfer means 17 has a cylindrical peripheral surface 18 narrower than the width of the stripe. This relatively narrow surface 18 may be thought of geometrically as a band-like surface taken from a portion of the width of a wide circular cylindrical surface. The cylindrical peripheral surface 18 is chosen to be narrower than the stripe width because all coating compositions tend to spread somewhat upon application, and this is true of the compositions used in accordance with the present invention although their lateral spreading is moderate and closely controllable. With the present method a lateral spreading of about $6 to V inch on each side of the peripheral surface is usual, so that the width of the peripheral surface may be about 0.050 inch to obtain a stripe 0.100 inch wide. It is remarkable that the striping operation can be controlled, as discussed hereinbelow, to maintain the over-all width of the dried stripe within close tolerances after a suitable width has been chosen for the peripheral surface 18 of the transfer means.

The transfer means 17 may take the form of any of numerous structures having such a cylindrical peripheral surface. It may be, for example, a biconical structure in which the surface 18 is a flattened portion at the junction of the bases of two cones superimposed base to base, this structure having an axis passing through the two apices. It may be alternatively the outside surface of a rim supported by spokes about a central axle. As indicated herein more specifically by way of example, however, one form which the transfer means 17 may take is a solid circular disk having a width throughout equal to the width of the surface 18. As mentioned hereinbelow, two additional similar disks are provided side by side, because in this instance it was desired to form simultaneously three separate stripes side by side. It will be evident that still another form which the transfer means 17 might take could be a relatively wide cylindrical roll, perhaps about one inch Wide and substantially smaller in diameter than the disk 17, having a peripheral raised rim portion the edge of which would provide the peripheral surface 18 of the desired diameter; several such raised rim portions could be provided to serve for applying each of the several magnetic stripes. Obviously if several peripheral surfaces are to be provided so as to form several stripes side by side, the widths of their individual peripheral surfaces could be different if it were desired to form stripes of different widths. Also an obvious equiva lent of a continuous circular or cylindrical peripheral surface such as that of disk 17 would be such a surface having a break, which will produce a stripe having gaps or discontinuities formed once each revolution of the transfer means 17. Likewise a plurality of such breaks or discontinuities in the disk would cause a corresponding number of gaps for each revolution of the disk and could result in the formation of a dashed stripe.

The disk or other transfer means 17 is arranged with its peripheral surface disposed closely adjacent to the one web surface opposite the guiding surface 13. The transfer means 17 is supported rotatably on a central axis 19. This axis lies in a plane parallel to the one web surface passing the guiding surface 13 but is perpendicular to the aforementioned direction of motion thereof. It follows that the axis 19, in the embodiment seen in FIG. 1, is aligned parallel to the axis of the impression roll 16. In practice the peripheral surface 18 of the disk often is disposed so that it barely touches the one surface of the web 12.

The transfer applicator disk 17 is rotated about the axis 19 in the sense causing the peripheral surface 18 to move, while it is adjacent to and moving past the one web surface, in the direction opposite to the direction of motion of the web at that point. It may be seen, then, from FIG. 1 that the aforementioned opposite direction is toward the lower right in the particular arrangement illustrated. This is accomplished by effecting a clockwise rotation of the disk 17 as shown, and this rotational sense is indicated by the arrow alongside the disk 17. The mechanical provisions for effecting rotation of the various cylindrical surfaces and rolls shown in the drawings are conventional and of little importance to the present invention, and no detailed driving power arrangements are indicated in the drawings.

As the peripheral surface 18 of the transfer means 17 approaches the one web surface, a coating composition of an aqueous synthetic latex dispersion which contains particles of ferromagnetic iron oxide in suspension and a thickening agent is applied to the peripheral surface 18. Due to the rotation of the transfer means 17, the coating composition so applied and is transported on the peripheral applicator surface 18 and is transferred to and deposited on the one surface of the paper web 12 as the web moves past the guiding surface 13. One suitable form of an arrangement for handling the aqueous coating composition and applying it to the transfer means 17 is indicated generally at 21 in FIG. 1 and will be discussed in some detail hereinbelow. Ordinarily, this coating op eration is carried out with the transfer means arranged, and its peripheral surface 18 disposed, so that the latter surface is wiped clean of the coating composition as the rotation of the transfer means moves it past the web. Good results have been obtained when the speed of rotation is such that the peripheral surface 18 moves past the web at the same linear speed as the speed at which the web is moving over the guiding surface 13, the web surface and the peripheral surface moving in opposite directions as a result of the sense of rotation of the disk 17 indicated by the arrow alongside the disk. Web speeds of at least several hundred feet per minute are practical. At high web speeds it may be found desirable to move the peripheral surface 18 at a linear speed even greater than the web speed to obtain adequate transfer of the striping composition. As noted hereinbelow, some of the coating composition also tends to be carried by the side surfaces of the transfer means immediately adjacent to its peripheral surface 18. Any portions of the coating composition adhering to these adjacent surfaces which are not transferred to the web surface should be cleaned from the transfer means 17 before its peripheral surface 18 rotates around to return to the point Where coating composition again is applied to it; one Way of insuring satisfactory cleaning of the transfer means will be described hereinbelow.

Aqueous coating compositions of many different formulations containing a synthetic latex of plastic or resin material, suspended ferromagnetic iron oxide particles, and a thickening agent may be used successfully in the method of the present invention. However, in order to obtain enough actively useful ingredients per unit volume of the composition for efficiency of application to the web, and also to provide a composition adequately thick or viscous and having in other respects good handling and transfer characteristics, it has been determined to be highly advisable that the coating composition with the aqueous vehicle should contain at least 7.5% by weight of discrete resin particles in the form of the aforementioned synthetic latex dispersion, at least 20% by weight of the ferromagnetic iron oxide particles in suspension, and at least 0.4% by weight of the thickening agent. Among suitable thickening agents may be mentioned such materials as polyvinyl alcohol, which forms a resin solution in water, or hydroxyethyl cellulose, which is a non-ionic water soluble ether of cellulose. Particularly good results have been obtained, however, with the use of a water soluble algin as the thickening agent. Any of these thickening agents may be added, during its formulation, to the aqueous composition as dry powders, each in approximately the same weight ratio relative to the weight of the entire coating composition.

In view of the vital role played by the coating composition in forming a magnetic stripe on a paper web in accordance with the present invention, the formulation of the coating composition will be discussed now in detail. Particular reference will be made to magnetic coating compositions containing the aforementioned minimum weights of the latex resin particles, of the iron oxide particles, and of a thickening agent in the form of a Water soluble algin, these being the preferred compositions by reason of their especially advantageous characteristics and superior utility as a striping formulation in the method of the invention.

The magnetic coating composition comprises an aqueous vehicle which is essentially water. The vehicle ordinarilyis essentially free of dissolved organic materials other than dispersing and thickening agents of the types dis cussed hereinbeiow. Aqueous coating compositions containing dispersed or suspended particles generally are provided with one or more dispersing agents, which suitably may be of the non-ionic type. Such dispersing agents, as is well known, are not added to provide any thickening action and so may be distinguished from the thickening agents already mentioned. A number of dispersing agents are mentioned hereinbelow.

The aqueous vehicle of the magnetic'coating composition also contains at least 7.5% by Weight of discrete resin particles in the form of a synthetic latex dispersion. In other words, an amount of the magnetic coating compo sition weighing pounds contains at least 7.5 pounds of the resin particles, the latter being taken on a solids or dry basis. A latex by itself is a fluid of generally milklike appearance in which small globules of approximately spherical particles of a hydrophobic polymeric material are suspended in water. the term originally was applied, is an emulsion or colloidal dispersion of rubber particles in water. The synthetic latex dispersions which form a part of the formulations used in the method of the present invention, and which are commonly identified as latex systems by the trade, are related in their physical characteristics to the rubber latices and contain small resinous particles in dispersion. The ultimate size of the discrete resin particles ranges in different cases from the smaller colloidal sizes of 0.01 to 0.1 micron, through the larger colloidal sizes of the order of 10 millionths of an inch (0.25 micron) in diameter, to sizes above the colloidal range, somewhat over 1 micron and occasionally over 2 microns. The socalled resin solutions of hydrophilic resins, such as aqueous polyvinyl alcohol, on the other hand, are not satisfactory if used as a substitute in place of the latex in the aqueous magnetic compositions employed in the striping method of the present invention. Resin solutions may not be true solutions in the strictest sense, but they containresin substances in such a fine state 'of subdivision that they are essentially homogeneous in structure and clearly distinguished from the synthetic latices; even when quite concentrated and viscous, resin solutions are clear under ordi- The rubber sap latex, to which.

be preserved in the stripe as it dries.

nary illumination and do not have the milky or opaque character of the synthetic latex dispersions. Since the synthetic latices do not contain resins in dissolved or quasi-solute form, they tend to be much less viscous than the resin solutions for a given concentration as computed on a dry solids basis. Synthetic latices, suitable for providing the aqueous vehicle of the compositions used in the method of the invention, as ofiered on the market, generally contain dispersing agents, and in some instances magnetic coating compositions of sutficient stability may be obtained without adding more of the dispersing agent or an additional dispersing agent. A number of resins are synthesized by emulsion polymerization techniques from the monomer or monomers in situ in the aqueous vehicle to produce latex dispersions which are suitable, in their forms as so produced and sold, for inclusion in the coating composition.

The aqueous vehicle further contains at least 20% by weight of ferromagnetic iron oxide particles in suspension. The reddish brown ferric oxide, Fegog, is ferromagnetic and may be used. Particularly suitable for this purpose, however, is the black ferroso-ferric oxide, Fe O which may be represented for convenience of description either as the oxide or as a salt, ferrous ferrite. It will be referred to herein as ferroso-ferric oxide regardless of the actual molecular structure which is characteristic of this oxidic material in crystalline form. The particle size should be small enough to maintain the ovide in fairly stable suspension in the aqueous vehicle containing the resin particles and dispersing agent. Ferroso-ferric oxide is obtainable in finely divided forms in which the particles are generally cubic in shape or in which they are acicular. The latter form is preferred and is obtainable under the trade designation lRN-l from C. K. Williams & Company, Easton, Pennsylvania. In this product the elongated particles have an average size of less than one micron; in a typical lot, less than 0.2% by weight is over 5 microns in diameter, while 99% by weight are smaller than 3 microns, 96.4% smaller than 1 micron, 91.6% smaller than 0.6 micron, and 57.2% smaller than 0.4 micron.

For good coating properties at high magnetic oxide loadings it has been found to be important that the aqueous vehicle should contain additionally a thickener. Several specific examples are mentioned hereinabove. The preferred thickening agent, a water soluble algin, may take the form of sodium alginate or ammonium alginate. These are available as powders which dissolve, or become finely colloidally dispersed essentially as a solute, in the vehicle. The algin serves several purposes in the coating composition. it acts as a thickener; such a thickened aqueous composition containing an amount of water giving a desirable viscosity does not have an excessive tendency to spread laterally after coating and so is good for deposition of a stripe of magnetic material having a high magnetic response characteristic. The algin supplements the action of the non-alginic dispersing agent in preventing agglomeration of the dispersed materials, and it imparts a thixotropic property which aids in maintaining the solid particles in suspension by establishing a viscous or quasi-gel structure when the composition is at rest while permitting ready flow when agitated and when moved through a coating apparatus. In forming a coating, the composition containing algin has good leveling properties; it flows well when applied as a stripe and then tends to leave a level deposit free of excessive thickness variations which otherwise might During drying, especially when the newly deposited stripe is raised rapidly to elevated temperatures, the presence of the algin inhibits the formation of cracks in the stripe and makes for a smoother surface. The algin contributes to the function of the latex in forming a tough yet flexible film for the deposited stripe-shaped coating, and the algin also prevents excessive penetration of a paper web by the wet coating composition as it is applied to the web.

13 as The following example is a preferred formulation of the magnetic coating composition:

Wolf 8: Co., Passaic, NJ.) 0.5 Sodium polyphosphate, empirical formula 1lNa O.10P O .H O (Calgon sodium hexametaphosphate, Calgon, Inc, Pittsburgh, Penna.) 1.0

Polyethylene glycol monooleate, liquid dispersible in Water (Kessler Chemical Co., Philadelphia,

7 Penna.) 0.65 Water 250.0

In preparing the coating composition of the example set out above, the condensed naphthalene-sulfonate and the polyethylene glycol monooleate were stirred Well into the Water at room temperature. The algin, sodium henzoate, and sodium polyphosphate were mixed together dry until evenly distributed, and then were sifted into the liquid with rapid stirring to obtain a smooth, viscous solution. Thereafter the iron oxide was mixed into the solution, which was subjected to milling on a three-roll mill. Finally, the polystyrene-butadiene resin dispersion was added and mixed well in a change-can mixer. The coating composition may be stored for a week or more if kept well covered and cool. To facilitate mixing and dispersion, a portion of the total amount of water should be withheld at least until after the milling operation.

This formulation contains 309 pounds of water and 58.5 pounds of the discrete resin particles on a dry basis. In this formulation the polystyrene-butadiene resin particles are present as an aqueous polystyrene-butadiene synthetic latex'dispersion. When freshly made this coating composition has a Brookfield viscosity of about 18,000 centipoises (No. 5 spindle, 10 rpm. at 25 C.). It 200 pounds of Water were added instead of the 250 pounds indicated above at the'end of the table, the viscosity would be about 35,000.centipoisespwhile 300 pounds of the added water would give a viscosity of about 10,000 centipoises.v Adjustment of the aqueous vehicle to have an amount of water which gives a viscosity for the coating composition of between 10,000 and 35,000 centipoises is readily achieved with simple tests, and these limits have been found desirable for best results when used to form magnetic stripes. In the example set out above, the resin particles make up 10.8% of the total weight, the iron oxide 31.0% and the algin 0.61%. With 300 pounds of added water to approach the minimum desirable viscosity, these proportions become 9.9%, 28.4%, and 0.56% respectively, approaching more closely the minimum practically effective proportions, 'which are mentioned hereinabove, for compositions having the properties desired for use in striping operations of the type particularly contemplated. Regardless of water dilution the ratio of iron oxide particles to resin particles on a dry basis is 2.86. These magnetic coating compositions are notable for the liberal amounts of magnetic materials which can be deposited; thus the weight of iron oxide particles, and particularly of the ferroso-ferric oxide, in any case can and should be at least twice the weight of resin particles on a dry basis. This ratio is particularly notable for aqueous compositions in view of the good flow characteristics of the composition, making it readily possible to form a narrow striped coating which nevertheless is held on the web in a highly adherent, coherent, and resilient mass when dried. Moreover, the composition has such good flow characteristics that a dried coating in the form of a stripe readily may be held to remarkably close tolerances in its width dimension.

The oxide material included in the composition of this example has good inherent characteristics for magnetic storage with a coercive force of 300-350 oersteds, a remanence of 2,0002,200 gauss, and a saturation flux of 3,7004,200 gauss, measured with a field of 1,000 oersteds at 60 cps. The polystyrene-butadiene synthetic latex dispersion used in the example has a viscosity of 25 to 27 centipoises at room temperature, a specific gravity of 1.015, and particle sizes within the range of 0.1 to 0.01 micron. The principal dispersing agent is considered to be the condensed naphthalene-sulfonate. The dissolved sodium polyphosphate is a dispersing agent and a sequestering agent for polyvalent metallic ions and is used to improve the physical properties of the composition. The polyethylene glycol monooleate used in the formulation oi the above example is the monoester with oleic acid of a polyethylene glycol having an average molecular weight of 380 to 420; this liquid ester has a freezing point of 4 to C. and a specific gravity of 1.13, and is a non-ionic surface active agent which further improves the characteristics of the composition.

The sodium benzoate dissolved in the aqueous vehicle acts as a preservative. A further addition of casein in an amount equal to between 2% and 3% by weight of the dry latex solids is recommended as a protective colloid for the latex. It also may be beneficial to include in the latex, used in formulating the coating composition,

an antifoaming agent, such as pine oil, octyl alcohol, or

an emulsion type silicone complex, in rather sparing amounts of the order of 0.2% of the weight of the latex. The latex resin and a dispersing agent or agents which are mutually compatible and are compatible with the other components of the coating composition may be chosen with a minimum of experimentation in the light of known precepts and of the discussion hereinabove, with help in many cases from the trade literature. Choice of dispersing agents, in addition to the thickening agent mentioned hereinabove, may depend on the nature of the synthetic latex used. For example, alternative dispersing agents, such as a sodium salt of a naphthalene-sulfonic acid condensed with formaldehyde, sold as Tamol N by Rohm & Haas Co., Philadelphia, Pennsylvania, or such as the sodium salts of certain carboxylated polyelectrolytes as available on the market, may be included. Such materials in quantities of the order of 250 parts by weight of the dry material per million parts of the coating composition ordinarily sufiice to provide a reasonably stable formulation, especially in the presence of the other materials mentioned hereinabove, which also contribute to keeping the resin and the iron oxide in a well dispersed state.

Other synthetic latex dispersions may be used instead of a latex of polystyrene-butadiene resin particles. A polyvinyl acetate latex dispersion of polyvinyl acetate resin particles dispersed in water may be included in the formulation. This resin dispersion may have coarser particles than do many synthetic latices, perhaps mostly in the range above one micron, but nevertheless is classified as a synthetic latex. Alternatively, a polyvinylidene chloride latex may be used. Also particularly suitable are some of the acrylic latex dispersions of acrylic resin particles. Acrylic resins, also frequently identified as acrylate resins, are glasslike thermoplastic resins made by polymerizing esters of acrylic or methacrylic acid (as methyl methacrylate). Excellent results have been obtained, for example, when, in place of the polystyrenebutadiene latex of the above example, there is substituted an equal total weight of a mixture made up of large proportions of two acrylic resin latices also of about 50% solids content and available on the market for a number of years as Rhoplex 13-15 and Rhoplex B-60-A from Rohm and Haas Company, Philadelphia. According to published papers, the material known as Rhoplex 13-15" is an acrylic polymer emulsion, and Rhoplex B-60-A likewise is a polymerized acrylic emulsion; these particular materials have a total solids content of 46%, which give clear films of substances having molecular weights greater than 2,000,000 and approximately 1,250,- 000 respectively, both having an index of refraction of 1.48 and a specific gravity of 1.09. The acrylic resin latex product obtained by mixing these two latex materials, and other particularly suitable resin latices, advantageously are those which give, when dry, fairly high flexibility while still forming highly cohesive films which are free of tack and resistant to blocking (tendency to stick to another body of the same material when left in contact) and to smudging under dry conditions and also under humid conditions.

Magnetic coating compositions of the type described hereinabove are the subject of the concurrently filed application for Letters Patent of the United States Serial No. 777,558, filed in the name of Charles I. Levine and assigned to the same assignee as the present invention.

After the coating composition is deposited as a stripe on the one surface of the web 12 by the transfer means 17, the web, carrying the wet stripe of the magnetic composition transferred from the peripheral surface 18, is subjected to drying conditions at elevated temperatures to provide a deposit free of tack and resistant to blocking and smudging under dry and under humid conditions. A great number of alternative procedures are available for carrying out the drying operation; the web is subjected to heat for drying the stripe, thus providing a dried, stripeshaped deposit high in ferromagnetic material and having the other desirable characteristics just mentioned. As an example, the drying may be effected by warm air in a large oven such as that represented at 22 in FIG. 1. Drying air is circulated through the oven 22 by a blower 23 connected to the oven by a hot air supply duct 24, within which the air passes over a number" of radiators, designated collectively by the reference numeral 26, which may be heated by superheated steam. Some of the air leaving the oven is recirculated by passing through a return duct 27 back to the blower 23. Moisture is removed from the system by bleeding some of the air passing Within the return duct 27 through an exhaust port 28, which is provided with a splitter damper, not shown, within the duct 27, and relatively dry room air is permitted to enter the circulating air system to replace the air thus exhausted.

The web entering the oven 22 is indicated at 29 in FIG. 1, and it leaves the oven at 31. A series of idler rolls within the oven 22, of which only several are in dicated schematcally in FIG. 1, permits the web to follow a long, up-and-down path while passing through the oven. This path may be, for example, as much as 200 feet in length to eifect complete drying at high 'web speeds without using excessively elevated temperatures of the heated air. approximate range of to C. with good results.

The best way to determine when sufficient drying is being obtained is to adjust the air temperature, the velocity at which the warm air is circulated, and other variables of the oven-drying procedure so as to obtain just enough drying action to render the deposited stripe material free of tack and resistant to blocking and smudging, as mentioned hereinabove and as determined by routine examination of the dried stripe on the web emerging at 31. The drying of the wet stripe also tends to remove some of the residual moisture from the paper web itself, and a portion of such removed moisture even may be replaced by carrying out subsequently a mildrehumidficaton of Warm air has been used within the Y 'the web, but this incidental drying of the web has been found to be beneficial in standardizing the dimensions and other characteristics of the substrate carrying the stripe.

After the drying, the surface of the web carrying the dried stripe is rolled to obtan at least a 20% reduction in the over-all thickness of the web and the dried stripe, making the stripe dense and smooth yet coherent and adherent to the web. This can be done by passing the web, after it leaves the oven at 31, between two large squeeze rolls 32 and 33, which may be driven, in the senses indicated in FIG. 1 by the arrow alongside each roll, so that their surfaces move in the same direction and at the same linear speed as the web passing between them.

Alternatively, the squeeze roll facing the striped web surface may rotate at a different speed to obtain increased calendering effect. Good characteristics in the rolled stripes have been obtained, for example, when the rolls were adjusted so that paper 0.0062 inch thick carrying a dried stripe 0.0045 inch thick was reduced to a thickness, measured over paper and stripe together, of 0.0076 inch, :1 reduction of about 0.0031 inch, or 29%. Roughly half of this total reduction in thickness appears to have occurred in the coated stripe and roughly half in the underlying paper web. Minor deviations in thickness which may occur in the coating operation are compensated for in the squeeze-rolling operation.

The rolling operation preferably should be carried out with the surface portions of the dried stripe maintained at a temperature providing substantial thermoplasticity in the material of such surface portions. It will be appreciated that the resinous components of the coating composition, such as the resin particles of the synthetic latex used in the composition, ordinarily are thermoplastic when dried, and desirable surface temperatures may be estimated from the softening point of the resinous material. Tne management of temperature in the rolling operation depends on the extent of the cooling of the aforesaid surface portions between the drying operation and the time of contact with the squeeze rolls. It may happen that, after drying, the web enters the squeeze rolls at approximately the preferred temperature for rolling. It may well be the case, however, that the surface portions of the stripes are too cold for optimum rolling. in such cases, the rolling advantageously may be carried out with heating of the roll which presses against the one striped side of the web. The roll may be heated by steam through a conventional arrangement, not indicated in FIG. 1. Rolling under the preferred temperature conditions leaves the stripe with a particularly smooth, well polished surface which is effectively non-smudging when rubbed while wet. This last-mentioned property may be tested by rubbing the wet finger back and forth across the wet stn'pe several times with moderate manual pressure. If no appreciable black smudge appears beside the stripe, it will be recognized that its mechanical stability has been demonstrated to be appreciably higher than the minimum rub resistance indicated by a general resistance to smudging during ordinary handling under humid atmospheric conditions.

The web leaving the squeeze rolls 32 and 33 passes between a pair of slitter rolls 34 and 36 having conventional interacting cuttng or shearing surfaces for trimming off the edges of the web and establishing the desired width of the finished product and the desired spacing between the stripe and the margins. The slitter rolls are rotatably driven so as to aid the motion of the web and at a slightly higher linear speed. The one striped surface of the web then passes over a large chill roll 37, through the interior of which a coolant may be passed if it should prove to be desirable to effect a rapid cooling of the web at this point and thus terminate any tendency toward further drying.

The striped web then is pulled past the aforementioned feed roll 14, which itself feeds the web across a further short distance and over an anvil roll 38. A cutting roll 39, equipped with two diametrically opposed cutting blades 41 and 42, is mounted above the anvil roll 38 so that the blades 41 and 42 cooperate with the anvil roll to sever the web laterally twice per revolution of the cutting roll. The anvil roll 38 is driven in a sense aiding the travel of the web, and the cutting roll is driven so that the blades 41 and 42 match the direction and speed of the web as they pass over the anvil roll, the driving of the rolls 38 and 39 being indicated in FIG. 1 by arrows alongside the rolls. The effective radius of the cutting blades is chosen so that the web moves over the anvil roll a distance equal to the desired sheet length during one half revolution of the cutting roll 39.

A continuous conveyor belt 43 is located to one side of and below the top of the anvil roll 38. The belt 43 travels around a driven pulley 44 and an idler pulley 46 in a direction indicated by the arrow alongside the driven pulley 44 in FIG. 1. The cut sheets 47, 47 ejected from the anvil roll fall on the belt 43, which conveys them past the pulley 44 and drops them in stacked arrangement in a receiving box 48. It will be appreciated that it frequently may be impractical to store the striped paper in rolled form or in high stacks because of the thickness added to a limited width portion of the web by the stripe formed along the web. It will be evident, also, that rotary printing equipment to imprint any desired matter in conventional ink on one or both sides of the striped web, perforating equipment, corner-notching equipment, and the like may be interposed between the chill roll 37 and the feed roll 14, so that the sheets 47 can represent a finished product, such as ledger sheets, with at least one stripe thereon for the magnetic storage of numerical information, ready for sale as such.

Returning now to the arrangement for handling the aqueous coating composition and applying it to the transfer means, indicated generally at 21, many suitable means may be employed for performing the functions required of such arrangement. A more or less schematic representation of one such arrangement is shown in greater detail in FIGS. 2 and 3. A convenient quantity of the magic coating composition, formulated and stored as described above, is placed when ready for use in a supply tank 51. The composition passes through a supply pipe 52 into a recirculation tank 53 provided with a conventional automatic level-maintaining means represented schematically at 54; a suitable valve arrangement in the supply pipe 52 and a control connection from the levelmaintaining means 54, not illustrated in the drawings, are provided. The recirculation tank 53 has a conventional agitator mechanism 56 illustrated schematically at the bottom of the tank and provided with a driving bar 57, which is indicated by a double-headed arrow as being reciprocated or vibrated to move the agitator mechanism and maintain the components of the composition in the recirculation tank in a well suspended and dispersed condition.

The coating composition is removed from the tank 53 through a feed conduit 58, along which is arranged a pump 59 to move the liquid composition toward the point of application to the transfer means 17. As the liquid leaves the pump 59, it passes through afilter 61 where any grit or oversized agglomerated particles are removed. The liquid then passes into a nozzle supply conduit 62 mounted in a nozzle housing 63. The conduit 62 terminates in a nozzle 64, which may be cleared whenever necessary by reaming with a nozzle cleaner 66 carried in the housing 63.

The nozzle 64 directs a stream, designated 67, of the coating composition against the edge surface 18 of the disk 17 at a region remote from the point where the rotating peripheral surface 18 reaches the web 12. The edge surface preferably is permitted to carry all the coating composition which adheres to the disk 17 freely around to the web. The stream 67 is confined generally but not com- .13 pletely'to a plane perpendicular t'othe axis of the disk, and its velocity is adjustable by controlling the pump 59. The radial and tangential components of the direction of the stream as it strikes the peripheral surface 18 also are adjustable by appropriate setting of the position of the housing 63. These adjustments permit control of the amounts of the coating composition which adhere to the edge surface 18. As already mentioned, the stream 67 may spread as it strikes the disk 17 so as to place substantial amounts of the coating composition on the sides of the disk near its edge, and some of the amounts so placed are transferred to the web by the rather rapidly rotating disk. All these adjustments give a flexibility which results in accurate control of the thickness and width of the stripe deposited on the web, and control of the width can be maintained even when thick stripes are deposited. Thus the striping and drying procedures readily can provide in a single application a dried stripe at least 0.003 inch thick which contains sufficient magnetic material to serve as a good magnetic storage medium.

The amounts of the coating composition in the stream 67 which do not remain on the transfer means 17 are collected in a curved collector portion 68 of a return duct 69. The liquid flows back in the duct 69 and enters the top of the recirculation tank 53,.passing through a filter screen 71 affixed in the upperportion of the tank 53. The action of the agitator 56 maintains the coating composition in condition for're-use until it is recirculated by passing through the feed conduit 58.

A doctor arrangement 72 with a plurality of blades is provided for cleaning the sides of the transfer means 17 near its peripheral surface. This arrangement is supported by a bracket 73. It is discussed below in connection with the showing of FIG. 3.

The nozzle and disk arrangement is represented in greater detail in FIG. 3, which shows the nozzle supply conduit 62 entering the bottom of the nozzle housing 63. The specific form represented in FIG. 3 of the arrangement for handling and transferring the coating composition serves to apply three distinct longitudinal stripes simultaneously to the web 12. The three stripes pass through the drying, rolling, and subsequent operations described herein just as would a single stripe on the web. Thus, two additional transfer means in the form of similar disks 81 and 82 are arranged on the central axis 19 which carries the disk 17, the three disks being separated along the axis 19 by spacers 83, 83 of relatively small diameter. The end portion of the nozzle supply conduit 62 within the nozzle housing 63 serves as a manifold to supply coating composition not only to the nozzle 64 but also to two additional and similar nozzles 85 and 86, the three nozzles being disposed side by side and separated laterally, as measured at their center lines, by the same distances which separate the center lines of-the respective disks 17, 81, and 82. In addition to the nozzle cleaner 66, two additional nozzle cleaners 87 and 88 are provided in the nozzle housing 63 for cleaning the respective nozzles 85 and 86. Streams of coating composition from the latter nozzles are applied to the peripheral surfaces of the respective disks 81 and 82, in the same manner as the stream 67 applies the composition from the nozzle 64 to the periphery of the disk 17, with the result that the two additional wet stripes from the disks 81 and 82 are applied to the web 12.

As seen in FIG. 3, the doctor arrangement 72 has a pronged shape, with the sides of four prongs disposed to wipe the two sides of each of the three disks 17, 81, and 82 near the edges of the disks. As mentioned hereinbefore, this prevents accumulation of untransferred coating composition from the portions of the disks not wiped by the paper web itself.

In one example of a striped web produced by the method of the present invention, each of the three dried stripes was one tenth of an inch wide, and their center lines were located in this example at distances of 2.2, 2.6, and

3.0 inches from one side margin of the slit web. The stripes formed on the paper web by the method of the invention, as described hereinabove, are resilient, dense, smooth, strongly coherent and adherent to the web, and admirably suited for magnetic storage purposes. The stripes have a self-polishing characteristic and will'not rub off against a magnetic transducing head or cause excessive abrasion of the head.

While there have been described what at present are considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein Without departing from the invention. It is aimed, therefore, in the appended claims to cover all such changes and modifications which fall within the true spirit and scope of the invention.

What is claimed is:

-1. The method of forming a stripe of magnetic material on one surface of a relatively wide paper web, comprising: moving the other surface of the paper web in a predetermined direction over a guiding surface; rotating an applicator, having a cylindrical peripheral surface narrower than the width of said stripe and disposed closely adjacent to said one web surface opposite said guiding surface, about a central axis which lies in a plane parallel to said one web surface passing said guiding surface but which is perpendicular to said direction of motion thereof, said applicator being rotated about said axis in the rotational sense causing said peripheral surface to move past said one web surface in the direction opposite to said direction of motion of said web; applying to said peripheral surface as it approaches said one web surface an aoueous coating composition containing at least 7.5% by weight of discrete resin particles in the form of a synthetic latex dispersion, at least 20% by weight of ferromagnetic iron oxide particles in suspension, and at least 0.4% by weight of a water soluble algin; and subjecting the web, carrying a wet stripe of the magnetic composition transferred from said peripheral surface, to heat for drying the stripeand providing a deposit free of tack and resistant to blocking and smudging under dry and under humid conditions.

2. The method of forming a stripe of magnetic material on one surface of a relatively wide paper web, comprising: moving the other surface of the paper web in a predetermined direction over a guiding surface; rotating an applicator, having a cylindrical peripheral surface narrower than the width of said stripe and disposed closely adjacent to said one web surface opposite said guiding surface, about a central axis which lies in a plane parallel to said one web surface passing said guiding surface but which is perpendicular to said direction of motion thereof, said applicator being rotated about said axis in the rotational sense causing said peripheral edge surface to move past said one web surface in the direction opposite to said direction of motion of said web; applying to said peripheral surface as it approaches said one web surface a coating composition of an aqueous synthetic latex dispersion which contains particles of ferromagnetic iron oxide in suspension and a thickening agent; subjecting the web, carrying a wet stripe of the magnetic composition transferred from said peripheral surface, to heat for drying the stripe and providing with a single transfer from said applicator a dried stripe at least 0.003 inch thick, free of tack, and resistant to blocking and smudging under dry and under humid conditions; and rolling the thus-treated surface of the web carrying the dried stripe to obtain at least a 20% reduction in the over-all thickness of the web and the dried stripe, making the stripe dense and smooth yet coherent and adherent to the web.

3. The method of forming a stripe of magnetic material on one surface of a relatively wide paper web, comprising: moving the other surface of the paper web in a predetermined direction over a guiding surface; ro-

tating an applicator, having a cylindrical peripheral surface narrower than the width of said stripe and disposed closely adjacent to said one web surface opposite said guiding surface, about a central axis which lies in a plane parallel to said one web surface passing said guiding surface but which is perpendicular to said direction of motion thereof, said applicator being rotated about said axis in the rotational sense causing said peripheral surface to move past said one web surface in the direction opposite to said direction of motion of said web; applying to said peripheral surface as it approaches said one web surface an aqueous coating composition containing film-forming resin particles in the form of a synthetic latex dispersion, at least 20% by weight of ferromagneticv iron oxide particles in suspension, and a thickening agent; and subjecting the web, carrying a wet stripe of the magnetic composition transferred by a single application thereof from said peripheral applicator surface, to heat for drying the stripe and providing a dried deposit at least 0.003 inch thick, free of tack, and resistant to blocking and smudging under dry and under humid conditions.

4. The method of forming a stripe of magnetic material on one surface of a relatively wide paper web,

comprising: moving the other surface of the paper Web in a predetermined direction over a guiding surface; ro-

tating an applicator, having a cylindrical peripheral surface narrower than the width of said stripe and disposed closely adjacent to said one web surface opposite said guiding surface, about a central axis which lies in a plane parallel to said one web surface passing said guiding surface but which is perpendicular to said direction of motion thereof, said applicator being rotated about said axis in the rotational sense causing said peripheral surface to move past said one web surface in the direction opposite to said direction of motion of said web; applying to said peripheral surface as it approaches said one web surface an aqueous coating composition containing at least 7.5% by weight of discrete film-forming resin particles in the form of a synthetic latex dispersion, at least 20% by weight of ferromagnetic iron oxide particles in suspension, and a thickening agent, the Weight of the iron oxide particles being at least twice the weight of said film-forming resin particles on a dry basis; and subjecting the web, carrying a wet stripe of the magnetic composition transferred from said peripheral surface, to heat for drying the stripe and p'oviding a deposit free of tack and resistant to blocking and smudging under dry and under humid conditions.

5. The method in accordance with claim 2, in which said rolling operation is carried out with the surface portions of the dried stripe maintained at a temperature providing substantial thermoplasticity in the material of said surface portions, said over-all thickness obtained after rolling being effectively constant.

6. The method of forming a stripe of magnetic material ,on one surface of a relatively wide paper web, comprising: moving the other surface of the paper Web in a predetermined direction over a guiding surface; rotating an applicator, having a cylindrical peripheral surface narrower than the width of said stripe and disposed closely adjacentto said one web surface opposite said guiding surface, about a central axis which lies in a plane parallel to said one web surface passing said guiding surface but which is perpendicular to said direction of motion thereof, said applicator being rotated about said axis in the rotational sense causing said peripheral surface to move past said one web surface in the direction opposite to said direction of motion of said web; applying to said peripheral surface as it approaches said one web surface an aqueous coating composition containing at least 7.5% by weight of discrete film-forming resin particles in the form of a synthetic latex dispersion, at least 20% by weight of ferromagnetic iron oxide particles in suspension, and a thickening agent, the weight of the iron oxide particles being at least twice the Weight of said film-form- 'ing resin particles on a dry basis and said composition containing an amount of water giving a viscosity of between about 10,000 and 35,000 centipoises; subjecting the Web, carrying a wet stripe of said magnetic coating composition transferred by a single application thereof from said peripheral applicator surface, to heat for drying-the stripe and providing a dried deposit at least 0.003 inch thick, free of tack, and resistant to blocking and smudging under dry and under humid conditions; and rolling the thus-treated surface of the web carrying the dried stripe to obtain at least a 20% reduction in the over-all thickness of the web and the dried stripe, whereby the stripe is made dense and smooth yet coherent and adherent to the web, and the over-all thickness after rolling is maintained effectively constant.

References Cited in the file of this patent UNITED STATES PATENTS 1,780,793 McLaurin Nov. 4, 1930 1,981,956 Jorgensen Nov. 27, 1934 2,075,620 MacKenzie Mar. 30, 1937 7 2,086,117 Case July 6, 1937 2,476,097 Kagen et al. July 12, 1949 2,608,127 1 Redfield Aug. 26, 1952 2,628,929 Persoon et a1 Feb. 17, 1953 2,633,431 De Sylva Mar. 31, 1953 2,688,567 Franck Sept. 7, 1954 2,699,408 Camras Jan. 11, 1955 2,748,015 Speed et al. May 29, 1956 2,862,845 Szegvari Dec. 2, 1958 FOREIGN PATENTS 759,486 Great Britain a Oct. 17, 1956 

2. THE METHOD OF FORMING A STRIPE OF MAGNETIC MATERIAL ON ONE SURFACE OF A RELATIVELY WIDE PAPER WEB, COMPRISING: MOVING THE OTHER SURFACE OF THE PAPER WEB IN A PREDETERMINED DIRECTION OVER A GUIDING SURFACE; ROTATING AN APPLICATOR, HAVING A CYLINDRICAL PERIPHERAL SURFACE NARROWER THAN THE WIDTH OF SAID STRIPE AND DISPOSED CLOSELY ADJACENT TO SAID ONE WEB SURFACE OPPOSITE SAID GUIDING SURFACE, HABOUT A CENTRAL AXIS WHICH LIES IN A PLANE PARALLEL TO SAID ONE WEB SURFACE PASSING SAID GUIDING SURFACE BUR WHICH IS PERPENDICULAR TO SAID DIRECTION OF MOTION THEREOF, SAID APPLICATOR BEING ROTATED ABOUT SAID AXIS IN THE ROTATIONAL SENSE CAUSING SAID PERIPHERAL EDGE SURFACE TO MOVE PAST SAID ONE WEB SURFACE IN THE DIREACTION OPPOSITE TO SAID DIRECTION OF MOTION OF SAID WEB; APPLYING TO SAID PERIPHERAL SURFACE AS IT APPROACHES SAID ONE WEB SURFACE A COATING COMPOSITION OF AN AQUEOUS SYNTHETIC LATEX DISPERSION WHICH CONTAINS PARTICLES OF FERROMAGNETIC IRON OXIDE IN SUSPENSION AND A THICKENING AGENT; SUBJECTING THE WEB, CARRYING A WET STRIPE OF THE MAGNETIC COMPOSITION TRANSFERED FROM SAID PERIPHERAL SURFACE, TO HEAT FOR DRYING THE STRIPE AND PROVIDING WITH A SINGLE TRANSFER FROM SAID APPLICATOR A DRIED STRIPE AT LEAST 0.003 INCH THICK, FREE OF TACK AND RESISTANT TO BLOCKING AND SMUDGING UNDER DRY AND UNDER HUMID CONDITIONS; AND ROLLING THE THUS-TREATED SURFACE OF THE WEB CARRYING THE DRIED STRIPE TO OBTAIN AT LEAST A 2/% REDUCTION IN THE OVER-ALL THICKNESS OF THE WEB AND THE DRIED STRIPE, MAKING THE STRIPE DENSE AND SMOOTH YET COHERENT AND ADHERENT TO THE WEB. 